This invention relates to pulse generating circuits. More particularly, this invention relates to circuits that can repeatedly generate powerful, high voltage pulses of extremely short duration. These types of circuits are critical to the development of ultra-high resolution radar and new spread spectrum communication modes, as well as many other applications requiring broadband radiation.
Much recent research has focused on laser-diode driven GaAs optical switches, but these devices have yet to switch reliably in less than 200 picoseconds, and their associated laser-diodes have repetition rate and reliability problems. Other methods of generating fast, low jitter transients include GaAs thyristors and magnetic shock lines, but GaAs thyristors are not commercially available, and magnetic shock lines require extremely high power levels.
Two existing diode related technoloties form the basis for the present invention:
Nonlinear transmission lines that utilize the nonlinear capacitance of reverse biased semiconductor diodes have been described in the literature, however they are operated at low voltages, usually around 10 volts. Their output pulses are not powerful enough for use in the radar and communication applications mentioned above.
Pulse generators exploiting a non-destructive "transit time" avalanche breakdown mechanism in ordinary diodes have also been developed. (This is an extremely rapid avalanche breakdown of the TRAPATT variety.) In 1979 the Soviets discovered that this mechanism could be used with diodes to make leading edge "pulse sharpeners" by causing the diodes to break down in a pulsed bias mode instead of using a continuous reverse bias as in the TRAPATT mode. The problem with these pulse generators is the avalanche mechanism has a drive requirement of 2-3 kV per nanosecond. Such a high drive requirement is generally supplied by UHF vacuum planar triodes, which are both expensive and impractical for many applications. Also, they need to be replaced periodically.
The widespread need for an inexpensive and practical pulse generator is filled by combining the above technologies in a truly unique way to make a device according to the present invention.